1. Field of the Invention
This invention relates to an aluminium alloy intended to provide a protective coating for surfaces which are subjected to extreme stress due to friction, with an aluminium matrix incorporating at least a soft phase and a hard phase, which hard phase contains at least one element from a first group of elements comprising chromium, iron, cobalt, copper, manganese, nickel, molybdenum, magnesium, niobium, platinum, scandium, silver, silicon, vanadium, tungsten, zirconium and/or carbides, silicides, nitrides, borides of the elements from the first group of elements or inter-metallic phases from elements of the first element group, and/or inter-metallic phases of aluminium with the elements from the first element group, and the soft phase contains at least one element from a second element group comprising silver, aluminium, gold, bismuth, carbon (Graphite), calcium, copper, indium, magnesium, lead, palladium, platinum, scandium, tin, yttrium, zinc and lanthanoides, the soft phase element being different from the hard phase element, and also relates to a coating primarily meant for friction surfaces made of an aluminium alloy, a composite material comprising a base and a surface layer applied on top of the base, as well as a process for manufacturing a composite material comprising at least a substrate and a surface layer applied on top, as well as the use of this aluminium alloy for producing a friction surface layer for friction surfaces and for coating components subjected to stress due to friction.
2. Prior Art
Coatings meant for components subjected to stress due to friction have to meet exceedingly demanding requirements. Firstly, the intention is to provide a coating susceptible to as little friction as possible, which is relatively soft and as a result, has the characteristics to adapt to wear and tear and at the same time is able to adapt itself to the mating component. Apart from this it should also possess very high mechanical and tensile strength, in order to be in a position to absorb static as well as dynamic vibration loads, thereby increasing durability and service life. Development in the automobile industry is tending towards higher specific performance in order to increase the efficiency in view of increasingly tough standards governing exhaust emissions, thereby making internal combustion engines more economical and environmentally friendly. A large number of components in internal combustion engines are affected by this development, such as radial bearings which are subjected to extreme stress due to very high torques and the ever increasing compression ratios needed to optimise the combustion process, for example in the case of a direct-injection turbo-diesel engine. Standard friction bearings are not designed to take such loads and stresses. The high efficiency of fuel injection systems used with these engines also means that components of the injection pumps and their measuring instruments are subjected to high stress, as are other components due to higher performance, such as piston rods, pins or rollers, which are subjected to sliding friction and have to meet the demands of higher mechanical loads. Very often, aluminium alloys are used in such cases because they represent a good relationship between the properties which can be achieved and the costs that have to be met.
DE 36 31 029 C2 describes an aluminium alloy containing tin and its application in a two-layered bearing material. Due to the addition of other elements like such as tin, silicon and lead, a structure is obtained due to tin and lead alloy particles which have been precipitated from the aluminium matrix, which are precipitated adjacent to the silicon particles. The bearing material is therefore intended to exhibit better properties, such as higher fatigue resistance and greater protection against friction.
DE 101 35 895 A1 describes an aluminium alloy which contains aluminium-silicon-iron ternary inter-metallic compounds and silicon particles in the form of hard particles. The anti-blocking characteristics are improved as a result without reducing fatigue resistance.
U.S. Pat. No. 4,471,029 describes an aluminium-based alloy which contains silicon and tin as the alloying elements, in which the majority of the silicon particles have a diameter of >5 μm. This is meant to increase fatigue and friction resistance.
DE 43 12 537 C2 describes a multi-layered coating of aluminium alloys with a base, intermediate and bearing coatings, in which the bearing surface is made of an aluminium alloy containing tin and silicon with a Vickers hardness of <50. This is meant to increase compatibility and tolerance as well as fatigue resistance.